Synchronizing signal separating circuit



Jan. 3, 1950 J, KUPERUS 2,493,353

NGHRONIZING SIGNA R Filed Feb. 8, A19,447 v2, Sheets-Sheet 1 1 I I jl??? 11 mlmlu 'WWW )wwf /ffm INVENTOR JAN KUPERUS Jan. 3, 1950 J.KuPERus 2,493,353

SYNGHRONIZING SIGNAL SEPARATING CIRCUIT Fild Feb. 8. 194'? 2sheets-sheet 2 -/NVASNTOR JAN KUPERUS HGENT Patented Jan. 3, 1950 UNITEDSTATES? PATENPIYA` OFFICE SYN CHRGNJ-IZING SIGNAL SERARATING;

CIRCUIT Jan. Kapel-11s Eindhoven, Netherlands, as'signor toHartfoi-dvNational Bank' andTrust Conr-4 pany, Hartford; Conn., as trusteeApplicationiFebruaryfS, 19M,-l Serial N o; 727,4681- InftheNetherlandsMarch 25, 1944- section 1, Public'L-aw .esogaugusta 194e Patent kexpiresMarch=25, 1964!l 1 Claim.` (Cl. IHS-7.3)

1 2; l This invention relates' to asystem and a re the imagesynchronizing pulsesand. interruption ceiverV for thetransmission andthe receptionrepulsesrhavingaV frequency. equal to the dine-rires-rvspectively of inanimatedor animated fimages', quency or. to a wholemultiple,1forexample twice; more particularly of television pictures,vin-Which of the line frequency.:v These interruption pulses:`systemsynchronization ofv the receiver picture were heretofore usedAsolelyhto control-the: saw-1 with that transmittedv is obtained-by meansof a tooth `generator `for. line scanning duringv the oc`signalvhavingline pulses and-image pulses whichV ourrence ofarrimage'synchronizingzpulsesarev interrupted once-or several timesbyinter- In. order that the invention-maybe clearly una, rupting pulses.dcrstood and readily carried into eifect;it'lwil1 According toacommon-method of-image synio now be set out more fully.vwithlreferencerto thel chronization in' televisionreceptionthe parts"of-y accompanying drawings, inzlwhich yis represented-i the incomingtelevisionu signal corresponding to one form of construction` of "a1receiverfsuitable the image are-iirst clipped Yand after that there' forvuse in a system for' transmitting television. maining part is suppliedto a network by which images according toithe;I invention. the pulsesfor synchronization of the imageare lo Fig. la represents the variationof lartelevision'` separated from the pulses used for the line'syn-fsignal of the kind used according tothe1inven-V chronization. Afrequently usedv networkV con tion. The full vertical lines, whichfareequidise sists of the parallel connection ofrtwo-branches tantly spacedapart from each other, coincide in; each of which is formed bytheseries-conneceach instance with thev leading. impulse-of'f'a'linetion cfa resistor anda condenser; the line pulses :fil pulse. The partof'. they signal'fshown between being derived acrossV the resistor ofone' branch; thepoints P and Q comprisestwo=lineipulses`that and theimagelpulses being derivedfacrossthe are' used rfor thesynchronizationnof the line condenser of the'other branch. scanning, andin addition twovparts vwhich cor-' This method has the disadvantagethat-the respondlt'o-the television image'of theiresp'e'ctive slope ofthe front of the image impulse is com'- 5 lines. An imageY pulseissh'own which extends paratively small, owing to which the yimage syn-v:from point Q to pointR. From R to S`the drawchronization does notalways start exactly at the ing shows two linev synchronizing' pulsesand two same moment, which is very troublesome partie. portions of theimagefcorrespondingA to the asularly when making use of interlacedscanning,` sociated line synchronizing pulses. since in this casein-general the lines of one 39 According tothe-'invention theimageipulseis frame do'not extend' midway between thelines interruptedbya number of interrupting pulses of the other frame: at a frequencyequal to the line frequency: the Now the present invention procures amethod trailing impulse of these interrupting pulses is of imagesynchronization, in which-"this evil is iniixed time-relation'with theleadingimpulse cured. 35 of the line pulses, consequently with theleading In the system, to which theinvention relates; impulseon whichthe line scanningis synchroit is common practiceto transmitz one ormorenized. -In the case ofl interlacedv scanning it 'is line synchronizingpulses during every image sufcient to maintain a fixed time relationbepulseyand toy avoid large current excursions to tween theinterruptingpulses of succeedingl imr apply them in theopposite sense soVas to create 40 age pulses; since inthis casethe twoframesalinterrupting pulses having a xed time relation ready occupy theircorrect relative positions: with respect to the line synchronizingpulses. Fig.- 1b represents the signal again; butv now Alternatelythere-maybe a time'relationshipesafter the image hasfbeenvcut 01T 'andthe signal tablished-between-therinterrupting pulses of suc'- H itselfhaspasse'dy through 'a reversing stage;v The" oeeding image pulsesyvithyrespect to one an- 4glatter is required in the present case, since-theother.v line pulses Y must" be' supplied"A i'nf a lpositive direc.1' Ina suitable form of constructionofa' trans' tion to the generatorproduc'zing"the' saw-tooth'. mitting'system according tothe inventionevery voltage for theline scanning, andi the leading image'pulse isinterrupted by pulseshaving a fre- F impulse of the initial-y pulse istraversedin-"a negquency equall tothe line frequency or to awhol'e Dative sense. multiple, for example twice the line frequency; Cursorilyitmay be: observed that 1in' several and for the image synchronization inthe retelevision systems' the imagefsignalv is suppressed ceiver usev ismade of oneormoreofthesepulssg immediately before and. after the image'pulse preferably' the viirst 'off' tha-interruptingpulsesa duringtransmission'. Frequently line'. 'pulses' It is commony to4l transmitsimultaneously with 50' lievi-nga double-4 frequencyf:areYtransmitted-noir Cil transmitted both before and after the image pulses.

In order to derive only the pulses for the line synchronization from thesignal represented in Fig. 1b, the signal is applied to adifferentiating network from which pulses as shown in Fig. 1c can beobtained. The positive peaks of these pulses, which coincide in eachinstance with the full vertical lines referred to above and consequentlywith the leading impulse of the initial line pulses, are used for theline synchronization,

According to the invention the pulses for the image synchronization may,for example, be obtained as follows. The signal shown in Fig. 1b isfirst of all applied to an integrating network whose output voltagevaries in the manner as shown in Fig. 1d. This voltage in excess of agiven threshold value is used to select denite impulses from the initialseries of pulses (see Fig. 1b). The said threshold value is indicated inthe gure by a horizontal dot-and-dash line. At T the output voltage ofthe integrating network exceeds this threshold value and from this pointthe selection can consequently take place. The period of selection laststill point U is reached, where the output voltage of the network againbecomes lower than the threshold value. Fig. le shows the period ofselection diagrammatically by a block line, whilst Fig. 1 f shows theimpulses selected from the initial series of pulses in this period.

- For the image synchronization the trailing impulse of the firstselected pulse is used, which pulse is designated V in Fig. lf. Themoment at which the trailing impulse of pulse V occurs is in fixed timerelation with the moments at which the leading impulses of the linepulses appear.

To permit the trailing impulse of the pulse V to be used as asynchronization impulse, the selected pulses are supplied to a reversingstage and subsequently to a differentiating network; the former isnecessary because a positive pulse must be used for synchronization. Thepulse output voltage of the differentiating network is used for theimage synchronization; the output voltage is shown in detail in Fig. 1g.From this figure it appears that the rst positive peak coincides withthe trailing impulse of the pulse V and also with one of the fullvertical lines indicating the moments of the line synchronization.

Fig. 2 represents a circuit arrangement by means of which the impulsesfor the image synchronization can be produced in the manner set outabove.

The television signal is supplied to the terminals I of t'ne circuit andtransmitted to the control grid of a tube `4 through a condenser 2 and aresistor 3.- This tube comprises two discharge systems 5 and 6 whichhave a cathode, a control grid and screen grid in common, but whoseanodes and a set of further grids are arranged separately. In additionthe control grid circuit of the system 5 includes a resistor 1, a diode8 and a parallel connection of a resistor 9 and a condenser III. Thenetwork composed by the elements 2, 3, 1, 8, 9 and I0 constitutes acircuit arrangement known per se for the separation of the image signalfrom the synchronization pulses.

lead of discharge system 5.

The signal shown in Fig. 1a is applied to the input terminals I and isapplied to the control grid of discharge system 5 through theintermediary of a condenser 2 and an isolating resistor 3. The controlgrid is biased through a gridleak resistor 'I by means of a negativevoltage derived from the shunt combination of a resistor 9 and condenserI0 interposed in the cathode Across resistor l there is shunted a diode8 having the cathode connected to condenser 2 to rectify the negativesynchronizing pulses and to charge condenser 2 to the peak value of thepulses with respect to the blanking level and stabilize the pulses inthe usual manner. During the occurrence of these pulses the gridpotential of discharge system 5 is therefore negative with respect tothe cathode of discharge system 5 by an amount equal to .the voltagederived across resistor 9. Grid current will iiow as soon as thepotential at the cathode of diode 8 rises above this voltage, in whichcase, however, the biasing potential on the grid of discharge system 5will still be equal to the voltage derived across resistor 9, since thisvoltage dierence exists across resistor 3. It is necessary to supply asignal in which the pulse height from the bottom to the blanking levelis larger than the biasing voltage derived across resistor 9.

At the control grid of the discharge system 5 there is consequently setup a voltage having the form shown in Fig. la, from which, however, theimage signals have been clipped. Consequently, at the resistor I Ilocated in the anode circuit of the system 5 a voltage as shown in Fig.1b is obtained. This voltage is supplied through a blocking condenser I2to an integrating network which consists of two resistors I3 and IG anda condenser I4 and whose output voltage is applied to the third grid ofthe discharge system E. A battery I5, connected in series with resistorI6, provides a negative bias by means of which the threshold value shownin Fig. 1d is realized.

The discharge system 6 conducts only when the positive voltage throughthe condenser I4 exceeds the threshold value (T-U in Fig. 1d). Hence,only the pulses shown in Fig. 1f can appear across resistor I1 locatedin the anode lead of discharge system 6. |These pulses are supplied to adifferentiating network consisting of a condenser IB and a resistor I9,whose output voltage, which is derived across the resistor I9, has theform shown in Fig. 1g. This voltage is used for image synchronizationand to this end it is applied to a saw-tooth generator (not shown) whichproduces the saw-tooth voltage for the vertical image scanning. Inaccordance with the adjustment of this saw-tooth generator thesynchronisation takes place on the first or on one of the next peakvoltages shown in Fig. 1g. Preferably, however, synchronization takesplace on the iirst peak Voltage.

It follows from what has been said above that the image synchronizationtakes place a fixed time after synchronizationof the line scanning. Inthe common circuit arrangements for the aforesaid purpose this is notthe case; in these circuits synchronization takes place by means of theimage impulse itself (shown in Fig. 1d) at the moment at which thisimpulse exceeds a definite threshold value. This moment (point T in Fig.1d) has no fixed position relatively to the preceding line pulses, sothat also the image synchronization is not in a fixed time relationshipwith the line pulses with all consequent aforesaid disadvantages. Alsowith the present invention the point T may move to and fro, but in thiscase the variable position of the point is of no importance since it isnot the point T but the trailing impulse of the selected pulse V whichdetermines the moment of synchronization. With the present invention thepoint T is, of course, not allowed in general to shift so far that theimpulse, on which synchronization should take place, is no longerselected. The point T, however, may shift through a very large marginbefore the synchronization fails. In the common method ofsynchronization, on the contrary,A the point T cannot be allowed toshift at all, particularly in the case of interlaced scanning.

However, a displacement of the point T readily occurs; since theposition of the point T is determined inter alia by the amplitude of theimage pulse, by any disturbances taking place in the image pulse and bythe degree of line pulse occurring in the image pulse. In practice, theline pulse is never completely separated from the image pulse.Consequently, voltages of the line pulses are always superposed on theimage pulse voltage. The presence of these superposed voltages isextremely detrimental to a good synchronization, particularly in thecase of interlaced scanning. In fact, the superposed line pulse voltagesare different for an even yand for an odd image pulse, since the placeof these image pulses relatively to the line pulses is different. In thecommon method this requires the synchronization of the even frame to bedifferent from that of the odd frame, so that the interlaced scanningmiscarries entirely or almost entirely. Attempts have been made toeliminate this disadvantage by transmitting line pulses of double theline frequency before, after and during the image pulse, thus toequalize as much as possible the two kinds of image pulses. The presentinvention, however, obviates this expedient.

Thus far the specication has mentioned only television signals and thedescription of the invention based on so-called positive modulation ofthe image. The invention, however, also applies to systems in whichtransmission with negative modulation takes place (the maximum amplitudeof the carrier wave corresponding with the peaks of the line pulses).

What I claim is:

A synchronizing circuit arrangement for a television receiver responsiveto signals comprising line synchronizing pulses and image synchronizingpu1ses comprising a plurality of interruption pulses occurring withinthe period of said image synchronizing pulses and appearing in fixedtime relationship with respect to said line synchronizing pulses,comprising an electron discharge device having a rst anode, a secondanode, a cathode common to said anodes, a rst control grid common tosaid anodes and interposed between said anodes and said cathode, and asecond control grid interposed between said second anode and said firstcontrol grid, said cathode, rst control grid, second control grid andsecond anode forming a transmission path, means to apply said imagesynchronizing pulses and said interruption pulses to said rst controlgrid, a network coupled between said rst anode and said second controlgrid for integrating image synchronizing pulses derived from said irstanode, and biasing means interposed in said integrating network tonormally close said transmission path for values of said integratingpu1ses below a predetermined threshold Value.

JAN KUPERUS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,210,523 Blumlein Aug. 6, 19402,224,134 Blumlein Dec. 10, 1940 2,273,546 Van Weel Feb. 17, 1942FOREIGN PATENTS Number Country Date 847,675 France Oct. 13, 1939 517,181Great Britain Jan. 23, 1940 529,790 Great Britain Nov. 28, 1940 869,945France Feb. 24, 1942

